HOUSTON (AP) – A Houston police officer is expected to recover after being shot following a traffic stop.

Houston media outlets report 47-year-old Officer Terry Smith was shot in the back Tuesday night near the Midtown area after the driver he pulled over had already left. Houston Police Department Chief Charles McClelland said Smith underwent surgery at Texas Medical Center and is in stable condition.

Capt. Dwayne Ready said Smith was putting away his ticket book when he heard a loud pop and felt some pain. Paramedics were called to the scene and found a gunshot wound in his back.

Police say they do not know who shot Smith, but they say it is likely the shooter was in a passing vehicle. They don’t believe the shooting and traffic stop are related.